: I've just replaced a frost-free spigot from one without an antisiphon to one with an antisiphon. When turned on, the new valve leaks water from behind the handle with the water seeming to come from the part of the stem where the handle screws into. But I could be wrong about the source of the water. The leaking is a low but steady flow, not a drip...drip.

: First, I tightened the large "nut" behind the handle (compresses the valve packing?) just a bit and initially it appeared to reduce but not eliminate the leak. Since, I've tightened it to the point where my wife has trouble opening and closing the valve, yet the leak continues.

: I've not used an anti-siphon valve before. Is this normal for this type of valve? Is the valve defective? Although new, should I try putting in more packing? Does it need to be replaced.The anti siphon acts as a vacuum breaker. In my experience, when you turn the valve on, at first water does leak out until its pressurized, then it stops. If this is not your problem, the packing nut itself could have a hair line crack in it and continues leaking.